This invention relates generally to the field of load-lifting cranes, and more particularly to a backhitch for such cranes.
The increased load-lifting capacities required of modern cranes have resulted in a large increase in crane size. Usually, this necessitates cranes being disassembled into smaller components for transport to jobsites. Crane disassembly and re-assembly is a difficult task due to the long crane booms and complex rigging systems typically encountered. The crane components, (i.e. the boom, gantry, backhitch, rigging, etc.), must be assembled and aligned correctly for the crane to operate safely and effectively.
A number of backhitches have been designed to help facilitate and simplify the task of assembling and disassembling cranes. Two of those designs are discussed in the following paragraphs.
Folding link backhitch designs are characterized by the backhitch having a folding portion therein. The folding portion of the backhitch rotates and folds to allow the gantry assembly to be lowered. The gantry assembly of this design, however, is unstable during initial lowering.
Telescopic backhitch designs are also known in the crane art. Often, the backhitch of these designs are formed of three separate links. The lower links, i.e. those closest to the crane bed, vertically telescope within a tubular structure on the crane bed or within themselves by means of, usually, a hydraulic cylinder. This telescopic movement causes the upper links of the backhitch and gantry to raise. This design is expensive, due to the numerous telescoping links and the hydraulic cylinders required, and is sometimes unstable due to the difficulty of balancing the hydraulic fluid flow to the cylinders on each backhitch leg.